(1) Field of the Invention
This invention relates to a polysaccharide polyol derived from Volvariella volvacea, a process for the preparation of this polyscaccharide polyol and an anti-tumor agent comprising this polysaccharide polyol as an active component.
(2) Description of the Prior Art
It is known that certain polysaccharides have an anti-tumor activity, but the relation between the structure and the anti-tumor activity has not been elucidated.
It also is known that polysaccharides having an anti-tumor activity can be obtained by oxidizing and reducing polysaccharides originating from certain fungi to convert them to polyols. For example, Japanese Unexamined Patent Publications No. 55-25409 and No. 56-34701 teach that when polysaccharides produced by Auricularia auricula-judae and a microorganism belonging to the genus Pestalotia are subjected to the above treatment, polysaccharides having an anti-tumor activity are obtained. Also in these polysaccharides, however, the relation between the structure of the starting polysaccharide or its polyol and the anti-tumor activity has not sufficiently been elucidated.
We already found that a polysaccharide obtained by alkali extraction of Volvariella volvacea has a strong anti-tumor activity (see Japanese Patent Publication No. 57-162121). However, if this polysaccharide is dried, it becomes hardly soluble in water under neutral conditions, and it cannot be deemed that the adaptability of this polysaccharide as an anti-tumor agent to the clinical treatment is sufficient.
We made research with a view to improving the water solubility of the polysaccharide disclosed in Japanese Patent Publication No. 57-162121 under neutral conditions without degradation of the anti-tumor activity, and as the result, it was found that if this polysaccharide is oxidized with an oxidant, especially periodic acid or a water-soluble salt thereof, and is then reduced, the water-solubility of the treated polysaccharide under neutral conditions is highly improved over that of the untreated polysaccharide and the anti-tumor activity is enhanced.